Process and furnace for expanding perlite



April 25, 1950 v w. E. JOHNSON ETAL 2,505,249

PROCESS AND FURNACEFOR EXPANDING PERLITE Filed Feb. 15, 1946, 2Sheets-Sheet 1 FIG.|

WILBUR E.JOHNSON ARMAN D R. BOLLAERT mvcu'roas Ap 25, 1950 w. E. JOHNSONETAL PROCESS, AND FURNACE FOR EXPANDING PERLITE 2 Sheets-Sheet 2 FiledFeb. 15, 1946 FIG.4

FIG.7

WILBUR E. JOHNSON ARMAND R. BOLLAERT .qih

INVENTORS FlG.lO

ORNEY Patented Apr. 25, 1950 PROCESS AND FURNACE FOR EXPANDING PERLITEWilbur E. Johnson, Hawthorne, and Armand R. Bollaert, Palos Verdes,Calii., assignors to Great Lakes Carbon Corporation, a corporation ofDelaware Application February 15, 1946, Serial No. 647,822

9 Claims.

The invention relates broadly to internally fired heat-treating kilnsthrough which the hot gases and the material being treated flow in thesame direction.

The invention relates more specifically to a horizontal, internallyfired kiln having a rotating heat-treating section interposed between astationary combustion chamber and a stationary collecting and dischargesection.

The primary objective of the invention is to provide a kiln adapted tothe inflation and vesiculation of pulverized rocks of volcanic originwhich contain water and which soften and intumesce when heated.

An objective of the invention is to provide a kiln for the above purposewhich is free from tendency to ball or aggregate the material beingtreated or to accumulate deposits of the expanded material.

An object of the invention is to provide a kiln of the type describedwhich has a large throughput capacity per unit of volume.

The invention will best be understood with reference to the attacheddrawings, showing an illustrative embodiment of the apparatus, togetherwith the following description thereof, in which Fig. 1 is a sideelevation of the complete apparatus;

Fig. 2 is a vertical, longitudinal section through the apparatus, thesupporting elements not being shown;

Fig. 3 is a ground plan of the apparatus;

Fig. 4 is an elevation of the left or firing end of the kiln, as on theline 44 of Fig. 1;

Fig. 5 is a cross section through the combustion chamber, as on the line5-5 of Fig. 1;

Fig. 6 is a cross section through the rotating element of the kiln, ason the line 6-6 of Fig. 1;

Fig. 7 is a cross section through the right hand or discharge element ofthe kiln, as on the line 'I! of Fig. 1;

Fig. 8 is a section on an enlarged scale of the joint between thestationary feed element B and the rotating treating element C;

Fig. 9 is a similar section of the joint at the right end of therotating section, and

Fig. 10 is a diagram illustrating a manner in which the kiln may beconnected with accessory elements.

Referring first to Fig. 1, the apparatus comprises four main elements: afiring section generally indicated at A, a feeding section B, aheattreating section C and a collecting section D. Section C rotates onits own axis: the remaining 2 sections do not rotate and are stationarywhile in use but are so arranged that they may be moved from and towardthe rotating section and each other for convenience in effecting repairsand for adjusting the gaps between the elements.

The firing section A consists of a flanged ring [0 of steel platecontaining a layer of hightemperature insulating material H and arefractory lining I2. At spaced points along the length and on oppositesides, projections from the shell, lined with refractory material,provide openings l3 and I4 for the insertion of tangentially arrangedoil or gas burners.

The outer end of combustion chamber I5 is closed by a head block l6having ports I! and I8 for the insertion of longitudinally disposed fuelburners, and provided also with two inspection ports I9 and 20. Whilethe head block may conveniently be separable from the ring to it isbolted to and supported by this ring.

The supporting means for the firing section is shown in side elevationin Fig. 1, in end elevation in Fig. 4 and in cross section in Fig. 5. Itconsists of two saddle plates 2| and 22, welded to the shell close toits ends, side plates 23 and 24 and a bottom plate 25. These plates arewelded at their edges to form a rigid box frame. The lower corners ofthe frame carry beating boxes 26-26 enclosing axles 2'l21. Flangedwheels 28-28, at the ends of these axles, ride on a track composed of apair of I-beams 2929 which extend the length of the kiln and for aconvenient distance beyond it at each end. These beams are permanentlyand rigidly supported, as

on a concrete pad.

The feed section B is similar in cross section to the firing section Aexcept for the omission of burner openings l3 and I4 and for theprovision of two inclined openings 30 and 3| along the upper centerline, through which the pulverized or fragmental material to beheat-treated is fed. This section is provided with a frame and wheeledsupport identical with that above described in connection with sectionA.

It is convenient and desirable that sections A and B should be separableand separately supported, but in use they are abutted end to end and maybe bolted together and suitable gaskets inserted to prevent leakage offire gases.

The rotatable heat-treating section C has a cylindrical shell 32 ofsteel plate, carrying two rigid trunnion rings 33 and 34. These ringsrest on pairs of adjustable trunnion rolls 35-3li which in turn rest oncross beams 36-38. The ring is. rotated in the conventional manner by ashaft 31 connecting two of the trunnion rolls and driven through asprocket 38 from any convenient source of power not shown.

Endwise movement of the rotating section is prevented by a pair of idlerrolls 39 horizontally mounted below the ring and engaging the sides oftrunnion ring 33 or 34.

The lining of the heat-treating section consists of an outer layer 40 ofhigh temperature insulating material and an inner layer 4| of .firebrickor other refractory. Through a substantial part of the length of thissection, rows 42 of firebrick project inwardly to form lifters for thecharge under treatment and to prevent it from sliding down the risingside of the cylinder.

The collecting and air-preheating section D consists of a short ring 43delivering into a downwardly converging section 44 which terminates in adelivery spout 45. These elements, which in use are continuouslysubjected to high temperature, are preferably formed of a heat-resistantalloy such as 25-12 stainless steel. Around element 44 is formed ajacket 48 of boiler or tank plate having an intake collar 41, a ventconnection 48 and a plurality of bafiies 49 by means of which a streamof cold air introduced at 41 is caused to take a circuitous coursethrough the jacket and to emerge at 48 in a highly preheated condition.

The collecting section, which of course is nonrotatable, is mounted on acarriage similar to that described in connection with firing section A.

As there is of necessity a leakage channel for fire gases at each end ofthe rotating section, where the adjacent fixed sections abut it, it isdesirable to use a heat-resistant steel such as 25-12 at these points,as illustrated in Figs. 8 and 9.

In Fig. 8, illustrating the joint between sections B and C. the cylindrcal ring In, of boiler or tank plate, has welded to its end a fiat ring49 of 25-12 plate, to which is attached a flange C of the same material.Similarly, the cylindrical shell 32 of the rotating section, of boileror tank plate, carries an end ring of stainless steel which in turn hastwo flanges 52 and 53 projected in opposite directions. The Z-shapedchannel thus formed reduces leakage to a minimum and the materials ofwhich its walls are formed resists buckling and distortion at hightemperature and permits the channel tobe reduced to narrow dimensionswithout bringing the plates into rubbing contact.

At the opposite end of the rotating section the tendencv toward leakageof fire gases is reduced by the lower pressure existing at the outletend of the kiln. It suffices to use at this point the joint illustratedin Fig. 9, in which the end ring 55, of stainless steel, is brought intoclose proximity to a stainless steel flange 56 formed at the end of ringsection 43' of the collecting section D.

A convenient manner of connecting up the assembly above described isshown on a much reduced scale in the diagram of Fig. 10.

The solids discharged by the kiln, together with the spent fire gases,pass from outlet 45 into a conduit 58 through which they are aspiratedinto a pebble trap 59 in which any heavy granular matter is separated.It may be desirable to admit a stream of cold air into this conduit, asby leaving an opening between its end and the discharge spout 45, toreduce the temperature in succeeding elements.

The gases laden with fine treated material pass from trap 59 through oneor more cyclone separators 60, in which the coarser suspended solids arecollected, and thence through conduit 6| to a conventional baghouse 62where the finest solids are recovered and the gases cleaned.

5 A suction fan or blower 63 creates a negative pressure in the baghouseand cyclone, thus producing the above described flow of gases throughthese elements. By regulating vent valve 64 the pressure at the outletend of the kiln (i. e., in collecting section D) may be controlled. Thepressure at this point will ordinarily be close to atmospheric but maybe very slightly negative to reduce or eliminate gas leakage.

A second fan or blower 65 takes in atmospheric air which is dischargedthrough conduit 66 into the intake connection 41 of the preheater. Theheated air discharged at 48 is conducted through a system of conduits 61to the burners at l3, 14, IT and I8. Spent fire gases from the baghousemay be introduced into the air supply through conduit 68 and valve 69 ifit is desired to increase the gas velocity through the kiln or tocontrol the temperature in the combustion chamber.

The requirement for a pebble trap in this assembly may be avoided byproviding an arcuate slot 10, of considerable length, at the lower partof element 43, closely adjacent the rotating section. A shield H is soarranged as to move over the slot and adjust its effective width.

Any unexpanded particles of perlite or of impurities which may occur inthe raw mineral tend to pass through this slot as they emerge from therotating section of the kiln. By maintaining a slight negative pressurein the collecting chamber, a current of air of controllable velocity isinduced through the slot, carrying any entrained light particles forwardto discharge nozzle 45 and allowing only the heavy waste particles topass through the slot and out of the system.

The inflation of glassy volcanic rocks of the type exemplified by themineral perlite may be made to produce filling and bodying powders ofthe most extreme lightness, weighing in some instances as little as fourpounds per cubic foot. This result is produced by the formation ofinnumerable extremely minute vesicles within each particle, thisvesiculation being due apparently to the presence of combined water inthe volcanic glass and to the evolution of steam at 5 temperatures atwhich the glass is plastic; 1. e.,

at the temperature of incipient fusion.

As the temperature of fusion lies not far above that of the plasticityrequisite to vesiculation, a desirably light product will be obtainedonly by maintaining the most exact control over the temperature to whichthe mineral particles are subjected. If the temperature be too low, theexpansion will be incomplete, while if it be too high, the mineral willbe fused, partially or entirely, the vesicular structure will be lostand the particles will aggregate into balls and tend to stick to thewall of the kiln. Either variation from the optimum increases the weightof the product and correspondingly reduces its value. 65 The optimumtemperature of treatment varies with the relative fusibility of theparticular lot or sample of mineral and may be anywhere between 1500 and2200 Fahr. But for any given specimen of the mineral there is an optimum7o temperature, determinable only by experiment, which lies closelybelow the fusing point, which must not be exceeded materially and whichshould be as rapidly and as closely approached as possible. It istherefore essential that the 75 furnace in which the expansion isconducted should be free from superheated zones and should have aslightly declining temperature gradient from the point at which themineral is introduced to the outlet end. a

The form of furnace shown is particularly adapted to the expansion ofperlite and similar minerals for a number of reasons. First, the use ofa combination of longitudinally and .tangentially arranged burnersproduces extreme turbulence in the combustion chamber and ensures thedelivery into the feed section of a column of flue gas at an absolutelyuniform temperature which is under complete control. This highturbulence ensures the completion of combustion and the attainment ofthe maximum temperature prior to in the fire gas stream. This costly andotherwise undesirable fine grinding is avoided by the provision of therotating section C. In feeding a mineral crushed to a much larger size,as for example inch and finer, the fine particles are expanded while insuspension in the fire gas stream and are swept through the rotatingsection without coming into contact with its walls. The largerparticles, which require more time for the high temperature topenetrate, subs de in the rotating section, in which they arecontinuously turned over and showered through the hot gases by thelifters 42. As these larger particles rise in temperature internally,they decrepitate, forming fine fragments and flakes which heat throughand expand very rapidly. As these finer particles become sufiicientlylightened by expansion to remain in suspension in the gas stream, theyare swept away into the collecting chamber and thus removed from thesystem. The funct on of the rotating section is thus to collect allparticles of such size as to be incapable of substant ally instantaneousvesiculation and to retain them in the zone of effective heating untilthey are suffic ently lightened by repeated spontaneous subdivision topass back into suspension.

Finally. the function of the preheating jacket surrounding thecollecting chamber is not merely to economize fuel by preheating the airsupply,

. but to a much more important degree is to maintain the end wall of thekiln, against which the stream of inflated solid particles impinges. ata temperature below that at which sticking and building up of depositscan occur. The sudden cooling of the spent gas stream, by even a fewdegrees. also tends toward the avoidance of any aggregation of theinflated particles in the outlet of the kiln.

While the actual dimensions of this structure may vary over a widerange. according to the throughput capacity desired, the relativedimenvent the deposition of the larger and heavier feed particles on thebottom of the stationary tube.

Finally, the rotatable section constituting the heat treating chambershould be of materially greater free cross section than the stationarytube, preferably at least in the ratio 1.5:1.0, to retard the gasvelocity and permit untreated or partially treated mineral particles toseparate from the gas stream before it reaches the discharge breeching.As above described, particles so separating in the heat treating chamberare reduced in dimensions and in relative weight by decrepitation andare brought back into suspension only when properly inflated, while iftheypass out of the heat treating chamber prior to full inflation, theycorrespondingly increase the weight and reduce the value of the product.

We claim as our invention:

1. The method of producing light weight powders from minerals of theperlite type which comprises: comminuting said mineral; establishing ahorizontally flowing stream of hot combustion gases; feeding a stream ofsaid comminuted mineral into said hot gas stream and therebyvesiculating the finer particles of said mineral while in suspension insaid gas stream; permitting larger and incompletely vesiculated mineralparticles to separate from said stream; collecting said separatedparticles and returning said collected particles into repeated contactwith said hot gases, downstream from said flame until said particles arebrought into suspension by decrepitation and vesiculation, and removingfrom the heating zone a stream of combustion gases having onlyvesiculated mineral particles in suspension.

2. The method of producing light weight granular products from mineralsof the perlite type which comprises: comminuting said mineral; burningfuel under conditions of turbulence and thereby produc ng a stream ofcombustion gases of equalized temperature; introducing a stream of saidcomminuted mineral into said gases at a. point downstream from the zoneof combustion and thereby expanding and vesiculating only the finerparticles of said mineral; moving the stream of combust on gasessubstantially horizontally at such velocity that the expanded particlesare carried in suspension from said zone of heating while the unexpandedand heavier particles remain therein, and continuously returning theunexpanded and heavier particles into said stream of combustion gases tobe further heated, said return being effected at points downstream fromsaid zone of combustion and without return of said particles into saidzone.

3. The method of producing light weight granular products fromcomminuted minerals of the perlite type which comprises: burning fuelunder condit ons of turbulence to produce a short hot flame and a streamof hot combustion products moving horizontally awayfrom said flame;feeding a stream of said comminuted mineral into said stream ofcombustion products at points downstream from said flame; maintainingthe temperature of said combustion products at such level that only thefiner particles of said mineral are expanded and vesiculated on firstentering said stream; removing the expanded particles in suspension insaid horizontally moving stream of combustion products, and retainingthe heavier unexpanded particles in motion, in contact with saidcombustion products and out of contact with said flame until they expandsumclently to pass into suspension and be carried away in saidhorizontally moving stream.

4. The method of producing light weight granular products from mineralsof the perlite type which comprises: reducing said mineral to particlesof unequal size; establishing a stream of hot combustion gases movinghorizontally to a point of discharge; feeding a stream of said mineralparticles into said gas stream at the end opposite said point ofdischarge; controlling the temperature and velocity of said gas streamto expand and vesiculate only the finer particles of said mineral, saidexpanded particles remaining in suspension in said gas stream and beingcarried therewith to said point of discharge; per-.- mitting theunexpanded and heavier particles of said mineral to subside from saidgas stream; collecting said heavier particles as they subside, andshowering said collected particles through said gas stream, downstreamfrom said flame, in a direction normal to the direction of gas flow,thereby causing said heavier particles to expand and vesiculate and topass into suspension in said gas stream and to be carried thereby tosaid point of discharge.

5. In a kiln for vesiculating comminuted minerals of the perlite type: ahorizontally disposed, internally fired, refractory tube so arrangedthat the combustion gases and the mineral feed travel therethroughconcurrently, and a breeching member arranged at the discharge end ofsaid tube, said member including a plate of stainless steel againstwhich said combustion gases and mineral particles suspended thereinimpinge, and means for passing an air stream over the rearward face ofsaid plate.

6. In a kiln for heat-treating minerals which decrepitate and vesiculatewhen heated: a, relatively narrow nonrotatable tubular combustionchamber provided with a tangentially arranged fuel burner to produceturbulence therein; an opening for feeding comminuted mineral throughthe wall of said combustion chamber near the discharge end thereof; arelatively wide, rotatable, horizontally disposed tubular heat-treatingchamber in which the velocity of the combustion gases is retarded topermit separation and retreatment of partially treated mineralparticles, and means for withdrawing from said heattreating chamber astream of spent combustion gases and treated mineral particles suspendedtherein while retaining partially treated particles within said chamber.

7. In a kiln adapted to the expansion and vesiculation of minerals ofthe perlite type: a nonrotatable combustion chamber; a nonrotatable feedchamber arranged to receive a stream of opposite that at which said feedconcurrent flow.

8. In a kiln adapted to the expan ion and vesiculation of minerals ofthe perlite ype: a tubular combustion chamber; a tubula extension ofsaid chamber; means associated with said extension for introducing afeed of a comminuted mineral into the hot gas stream from saidcombustion chamber at a medial point in the length of said kiln; aheat-treating chamber arranged to be rotated on a horizontal axis and toreceive the hot gases and mineral delivered by said tubular extension,and means for discharging the combustion gases and the expanded solidproduct from said heat-treating chamber in concurrent flow.

9. In a kiln for heat-treating minerals which decrepitate and vesiculatewhen heated: a. horizontally disposed, nonrotatable, refractory tubeprovided with fuel burners arranged to produce extreme turbulence andcomplete combustion in one end of said tube; means for feeding a streamof a comminuted mineral into the end of said nonrotatable tube oppositethat in which combustion occurs; a rotatable refractory tube alignedwith said nonrotatable tube and receiving hot gases and mineraltherefrom, said rotatable tube being provided internally withprojections for bringing mineral particles subsiding in said tube intorepeated contact with said hot gases, and means associated with saidrotatable tube for removing said hot gases and the heat-treated mineralproduct therefrom in concurrent flow.

rsandin WI'LBUR E. JOHNSON. ARMAND R. BOLLAERT.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 920,334 Huges May 4, 19091,800,247 Buckbee Apr. 14, 1931 1,976,208 Agthe et a1 Oct. 9, 19341,977,767 Klencke Oct. 23, 1934 2,116,030 Lindman May 3, 1938 2,129,523Butler Sept. 6, 1938 2,190,271 Powell Feb. 13, 1940 2,265,358 DenningDec. 9, 1941 2,306,462 Moorman Dec. 29, 1942 2,309,810 West Feb. 2, 19432,387,014 Gibson Oct. 16, 1945 2,421,902 Neuschotz June 10, 19472,435,395 Hopkins Feb. 3, 1948 FOREIGN PATENTS Number Country Date505,483 Germany Aug. 19, 1930 613,945 Germany May 28, 1935 OTHERREFERENCES Kozu: Thermal studies of obsidian, pitchstone and perlitefrom Japan," article in Science Reports, Tohoku Univ., Series 3, vol. 3,pp. 227- 230. Copy in Div. 3 in 252-378.

1. THE METHOD OF PRODUCING LIGHT WEIGHT POWDERS FROM MINERALS OF THEPERLITE TYPE WHICH COMPRISES: COMMINUTING SAID MINERAL; ESTABLISHING AHORIZONTALLY FLOWING STREAM OF HOT COMBUSTION GASES; FEEDING A STREAM OFSAID COMMINUTED MINERAL INTO SAID HOT GAS STREAM AND THEREBYVESICULATING THE FINER PARTICLES OF SAID MINERAL WHILE IN SUSPENSION INSAID GAS STREAM; PERMITTING LARGER AND INCOMPLETELY VESICULATED MINERALPARTICLES TO SEPARATE FROM SAID STREAM; COLLECTING SAID SEPARATEDPARTICLES AND RETURNING SAID COLLECTED PARTICLES INTO REPEATED CONTACCTWITH SAID HOT GASES, DOWNSTREAM FROM SAID FLAME UNTIL SAID PARTICLES AREBROUGHT INTO SUSPENSION BY DECREPITATION AND VESICULATION, AND REMOVINGFROM THE HEATING ZONE A STREAM OF COMBUSTION GASES HAVING ONLYVESICULATED MINERAL PARTICLES IN SUSPENSION.